- 25/05/2025
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00:00:00Hello, my name is Stephen Hawking, physicist, cosmologist, and something of a dreamer.
00:00:14Although I cannot move, and I have to speak through a computer, in my mind, I am free.
00:00:25Free to tour the universe, and tell the ultimate story.
00:00:33The story of everything there ever was.
00:00:40From the moment the cosmos began, to the creation of our world and everything in it, and beyond,
00:00:51to the far, far future, and the end of the universe itself.
00:00:57A journey through all of space, and all of time.
00:01:06Check it out.
00:01:21I spend a lot of time thinking about the universe, but I never get bored.
00:01:32After all, it's a pretty extraordinary place.
00:01:37This is the cosmos, at a very large scale.
00:01:43Each tiny point of light is an entire galaxy.
00:01:47Each a cluster of as many as 400 billion individual stars.
00:01:57This view of the universe is only possible due to the latest supercomputers.
00:02:02I find it indescribably beautiful.
00:02:06Uncountable billions of galaxies, forming a vast web stretching away in all directions.
00:02:16What's more, I never get over the fact that within this massive universe lies one perfectly
00:02:23ordinary spiral galaxy.
00:02:30Inside that galaxy exists a commonplace yellow star, orbited by eight planets.
00:02:45One of those planets lives a species that has only just worked out what a remarkable
00:02:51place the universe is.
00:03:00Us.
00:03:08We've discovered more about the cosmos in the last century than in all previous human
00:03:14history.
00:03:16Finally, we are solving the basic mysteries that have perplexed our ancestors for at least
00:03:23200,000 years.
00:03:27What I like above all is that the facts themselves are both breathtakingly elegant and surprising.
00:03:39We're living just as it dawns on us that the Earth and everything around us was made by
00:03:48the stars.
00:03:52Boiling furnaces of hydrogen gas like our sun made even the atoms in your eyelashes.
00:04:00We've worked out that the universe is almost unimaginably ancient.
00:04:05About 14 billion years old, and that it will continue to exist for at least twice that
00:04:12long.
00:04:14But without a doubt, the most remarkable fact of all is that the entire enormous universe,
00:04:26all the innumerable galaxies, even time and space and the forces of nature themselves
00:04:34simply materialized out of nothing.
00:04:44So now is a good time to be alive, I think.
00:04:48We may only be an advanced breed of monkey living on a small planet, but we are able
00:04:55to contemplate the universe as a whole, which makes us very special.
00:05:03My goal has always been simple, to work out how the universe works and why it exists at
00:05:09all.
00:05:12Luckily there are clues everywhere, and the most important one is right above our heads.
00:05:22Examine any patch of the night sky, even one as small as the head of a pin, and this is
00:05:29what you'll find.
00:05:32A tiny part of the vast web of galaxies.
00:05:37It's less than a millionth of what we can see of the cosmos from our little planet.
00:05:42But even this tiny sample is enough to find the clue, the key to the past, the present,
00:05:51and perhaps the future too.
00:05:55The clue is that seen from Earth, all these distant galaxies are slightly red in color.
00:06:03They appear almost as if we were looking through rose-tinted glasses.
00:06:10It's this very redness that reveals how the universe was born.
00:06:16And to show you why, I need a straight road and a noisy car.
00:06:25Listen to the sound as it passes by.
00:06:36As the car approaches, the pitch of its engine rises.
00:06:43As it goes away, the pitch of its engine falls.
00:06:51This phenomenon is called a Doppler shift, and the exact same thing happens with light.
00:07:00If our eyes were more sensitive to color, we could see that the car is actually very
00:07:05slightly blue as it approaches, and very slightly red as it goes away.
00:07:21The same rules apply in space.
00:07:25All distant galaxies are slightly red in color.
00:07:30So by the exact same piece of basic physics, they must all be moving away too.
00:07:38In fact, the whole universe is expanding in all directions, getting bigger and bigger,
00:07:46like a balloon inflating.
00:07:49I admit this sounds strange, but to cosmologists, it's like winning the lottery.
00:07:57Because to work out where the universe came from, all we need to do is to stop time and
00:08:05make it run in reverse.
00:08:11Rewind far enough, and everything gets closer together, a lot closer together.
00:08:18All the galaxies, in fact every single thing, converges to a single point, the start of
00:08:27everything 13.7 billion years ago.
00:08:42So it's quite simple really.
00:08:45Follow the clues, and we can deduce that a very long time ago, the universe simply burst
00:08:51into existence, an event called the Big Bang.
00:09:05But I'm afraid we have to stop a moment, before we get carried away by fire and noise.
00:09:13At the very beginning, the Big Bang actually happened in total darkness, because light
00:09:20didn't exist yet.
00:09:23To see it, we'd have needed some kind of cosmic night vision.
00:09:33But even this, a view from the outside, is impossible.
00:09:38Again, it sounds strange, but space didn't exist then either, so there was no outside.
00:09:48The only place there was, was inside.
00:09:58This early universe was a very strange thing indeed.
00:10:02There's still much I'd dearly love to know about it, but standard concepts of time or
00:10:07space don't really apply.
00:10:12It was just a very tiny, ultra-hot fog of energy.
00:10:22Then it expanded, with a tremendous flash of radiation, from smaller than an atom, to
00:10:34about the size of an orange, in less than a trillionth of a second.
00:10:39Almost no time at all.
00:10:46The universe simply inflated into existence, unfolding, unfurling, getting bigger and cooler
00:10:56with every passing moment.
00:11:04In one hundred seconds, it was as big as our solar system, trillions of miles across.
00:11:15While this was happening, the pure energy of the cosmos began to cool and create matter,
00:11:22in the form of countless trillions of subatomic particles.
00:11:29The first stuff there ever was.
00:11:35Half these particles were made of matter, the same kind of stuff which makes us.
00:11:41The rest were made of the opposite of matter, stuff called antimatter.
00:11:47When the two meet, they destroy each other in a flash of energy.
00:12:04It seems as if building a universe is a pretty wasteful process.
00:12:14Fortunately, there was just a bit more matter than antimatter.
00:12:19Just one in a billion particles of stuff survived.
00:12:29Which was lucky for us, because that residue is what our present-day universe is made of.
00:12:38You could say that we are made of the smoke of the Big Bang.
00:12:49By the time the cosmos was ten minutes old, it was already thousands of light-years in
00:12:56diameter.
00:12:57After that, everything spread out and cooled for about 330,000 years, when finally the
00:13:04fog cleared and the universe became visible.
00:13:20So that's how everything got going, which I think is a pretty fantastic story, and probably
00:13:27much stranger than anything our ancestors came up with by way of an explanation.
00:13:34But the next thing that happened, well, that's pretty spectacular too.
00:13:45This is the universe seen in extreme fast-forward, all 14 billion years in less than a minute.
00:13:58It shows how the universe changed from a cloud of gas into a place filled with perhaps a
00:14:04hundred billion galaxies, swirling in a vast, chaotic dance.
00:14:12What I love to get people thinking about is that all this had to be built, atom by atom,
00:14:21celestial engineering on a spectacular scale.
00:14:27So what drove this cosmic clockwork?
00:14:31I'd say it was the force of gravity.
00:14:41The idea of gravity was worked out by Sir Isaac Newton, who had the same job as me,
00:14:47here at Cambridge University, back in the 17th century.
00:14:55It supposedly dawned on him when an apple fell on his head.
00:15:08The apple helped him realize that all objects attract each other, and the greater the mass,
00:15:16the stronger the pull.
00:15:20These apples are attracted to the earth, and although you can't see it, the earth
00:15:26moves very slightly up, towards the apples.
00:15:35All things come together through the power of gravity.
00:15:43Gravity was created in the Big Bang, and has been at work ever since.
00:15:52It's what keeps you, me, and apples stuck to the earth.
00:16:06In the early universe, gravity had a much bigger role to play.
00:16:18Right after the Big Bang, the universe was just gas, almost perfectly spread out throughout
00:16:25space.
00:16:30Over the next 200 million years, gravity began to pull the gas back together, to produce
00:16:37the very first structures from which everything else would grow.
00:16:45But even this very nearly didn't happen.
00:16:55If it weren't for another stroke of cosmic luck, there would be no you, no me, no stars
00:17:03or planets, or anything at all.
00:17:09We know this because in 1982 a group of scientists, including myself, spent three solid weeks
00:17:16working it out.
00:17:19Although the calculations were hard, demonstrating what we discovered is easy.
00:17:25First, I need a nice flat floor, like this one, for example.
00:17:31This is the dining room in my college.
00:17:35I'm going to fill the place with lots and lots of ball bearings.
00:18:03These balls represent the matter of the early universe, a thin gas spread out evenly across
00:18:09the vast cosmos.
00:18:17Here's where luck comes in.
00:18:23If they're all the same distance apart, gravity pulls each ball the same amount in all directions.
00:18:32They stay perfectly aligned and precisely nothing happens.
00:18:38Fortunately, one of the basic rules of the universe is that nothing's perfect.
00:18:48Perfection simply doesn't exist.
00:18:57The early universe had a tiny unevenness that can be simulated by removing just five ball bearings.
00:19:14It may not look like much has changed, but to gravity, those missing balls create a giant opportunity.
00:19:25Gravity now pulls more strongly on one side of some of the bearings.
00:19:34The tiny irregularities in the sea of ball bearings have given gravity something to sink its teeth into.
00:19:42And this is exactly what happened back where we left the young universe.
00:19:51Parts of the sea of early gas were ever so slightly thinner than others.
00:19:57The less dense areas were like the gaps between the ball bearings.
00:20:05The denser parts of the sea of gas, where gravity was having its way, clumped together.
00:20:13And it was in these areas that all the stars and galaxies would form.
00:20:23The cosmos had taken its first step towards the beautiful place it is today.
00:20:30All thanks to irregularity, imperfections, a lack of order.
00:20:40The next time someone complains that you have made a mistake, tell them that may be a good thing.
00:20:46Because without imperfection, neither you, nor I, would exist.
00:20:5713.5 billion years ago, the universe was mostly hydrogen gas, with gravity doing what gravity does,
00:21:06which is to slowly pull it into vast clouds.
00:21:12Hydrogen is the simplest of gases, but it has a very special property.
00:21:18It's a tremendous source of power.
00:21:23Heat hydrogen to around 10 million degrees, and it begins to produce the energy that makes the stars shine.
00:21:32It supplies the universe with warmth and light.
00:21:37To see how this works, let's imagine we could make a small star here on Earth.
00:21:44First, we need plenty of hydrogen gas.
00:21:47About a sports stadium full would be perfect.
00:21:54Next, we need to imagine squishing this hydrogen together,
00:21:59just as gravity does in space.
00:22:08As the hydrogen compacts, the atoms of gas start bouncing off each other,
00:22:14and the temperature begins to rise.
00:22:19By the time it's compressed down to the size of a soccer ball,
00:22:25the hydrogen reaches the critical 10 million degrees,
00:22:33and a process called nuclear fusion begins.
00:22:39The hydrogen starts to fuse together, making a new, heavier material, helium.
00:22:49With every step of this tiny bump and grind, some matter gets converted into pure energy.
00:23:06We have created a miniature star.
00:23:20Of course, if this was a real experiment, you wouldn't want to go anywhere near it.
00:23:31The energy given off even from a star this small would be devastating.
00:23:40Back in the early universe, the same process happened for the first time on a much, much bigger scale.
00:23:52Gravity compressed the hydrogen gas clouds over millions of years,
00:23:58until deep in the centre, the hydrogen became hot enough for fusion.
00:24:09For fusion to occur.
00:24:24The first star burst into life, pouring its energy into the vast universe,
00:24:33a product of the laws of nature and the raw materials left over from the Big Bang.
00:24:41It was almost a thousand times bigger than our own sun, and burnt a deep blue.
00:24:49What's more, this star soon had company.
00:24:56The stars were turning on.
00:25:07This same process still happens in our sun, which is where we get the energy we need to live.
00:25:15But there was still a long way to go to get from this, to where we are today.
00:25:29You can't build a world like ours from simple gases, such as hydrogen and helium.
00:25:35You need all sorts of other elements.
00:25:39You need elements like oxygen and carbon and iron and many more.
00:25:45But we got lucky yet again, because the very same process that causes the stars to shine,
00:25:53also just happens to make materials like oxygen and carbon and iron.
00:26:09Stars, simply by accident, are giant factories.
00:26:20To see a star in action, let's imagine I could split one in half.
00:26:27Just as in the soccer ball star, the hydrogen atoms are fusing together,
00:26:33creating helium, which produces the star's energy.
00:26:39But helium is slightly heavier than hydrogen, so it sinks to the centre of the star.
00:26:47And now the helium atoms take centre stage.
00:26:57As they fuse together, they produce even more energy, and form yet another new element.
00:27:05Carbon.
00:27:08A vital building block of every living thing.
00:27:14The process repeats itself over and over, and the star becomes layered like an onion.
00:27:22A really big onion.
00:27:26The closer to the centre, the heavier the elements, like neon, oxygen and, last of all, iron.
00:27:35Now things change.
00:27:38Iron doesn't produce energy when it fuses, so the fire begins to go out.
00:27:46More and more iron builds up in the star's core, until almost all the remaining fuel runs out.
00:27:58Now gravity takes over, and squashes the star in on itself.
00:28:04As its core gets more and more compressed, its temperature soars,
00:28:10until it's over 100 times hotter than the core of our own sun.
00:28:21Finally, the star collapses, and explodes.
00:28:41This is a supernova.
00:28:48The death of a star, and the birth of something new.
00:28:57In these brief microseconds, a massive shockwave passes through the star.
00:29:05The blast is so powerful that it forces some of the iron to fuse into even heavier elements.
00:29:12And that's how heavy elements, such as gold, or platinum, or lead, are made.
00:29:20Forged in the heart of an exploding star.
00:29:25So if you have a gold ring, make sure you appreciate it.
00:29:30The metal was made in a blinding flash of light, billions of years ago.
00:29:36The finale of the process that produced the elements all around us today.
00:29:47It never ceases to amaze me that our bodies are constructed of the stuff of stars.
00:29:54And that our hearts beat because of the energy given off as those materials are made.
00:30:01But as magical as a star is, there are even more fascinating and powerful things in our enormous cosmos.
00:30:10The Milky Way
00:30:22Around 300 million years after the Big Bang, the early stars began to form galaxies.
00:30:29Which slowly took on a bewildering variety of shapes and sizes.
00:30:36Our galaxy, the Milky Way, is thought to be one of the oldest.
00:30:41Having started to assemble itself some 13 billion years ago.
00:30:49It's roughly 6,000 billion miles in diameter.
00:30:54And contains something like 200 billion individual stars.
00:31:00Nobody's quite sure exactly how many, since they can't all be seen from Earth.
00:31:05And anyway, it would take a long time to count them.
00:31:12Because all these stars were built by gravity, you could say gravity is the hero of the universe.
00:31:19After all, it turned a meaningless soup of gas into something of beauty and power.
00:31:28But like all interesting heroes, gravity has its dark side.
00:31:36Right in the centre of our galaxy lies an example of what happens when gravity rules unchallenged.
00:31:50A black hole.
00:31:58When I was in my twenties, I did some of the basic mathematics of black holes.
00:32:04But few people shared my fascination.
00:32:09These days, they are a popular subject.
00:32:15Physicists all over the world are studying black hole behaviour.
00:32:22We now know that black holes are not only fascinating in their own right,
00:32:28but that they play a fundamental role in the formation of galaxies.
00:32:33They also give us a glimpse of how the universe may end.
00:32:40A black hole forms when a large star, one, say, 20 times the mass of our Sun, comes to the end of its life.
00:32:52Such a star looks nothing like our Sun, because it's become unstable, convulsing violently as its death throes begin.
00:33:03Finally, it runs out of fuel and begins to shrink, getting denser and denser, hotter and hotter.
00:33:14But with a star this massive, there is no force in the universe capable of stopping the collapse.
00:33:22The core is so heavy that it just keeps on falling in on itself.
00:33:28Gravity is running wild.
00:33:33In just 15 seconds or so, the unstoppable force crushes the star from millions of miles in diameter to as little as 12 miles in diameter.
00:33:46All the mass that was in the star is still there, but its own weight keeps forcing it down smaller and smaller still.
00:34:00The temperature of the core soars to 100 billion degrees.
00:34:07The outer layers are blasted away in a massive supernova.
00:34:13But deep in the center, the core falls down what we call a gravitational well.
00:34:22The outer layers are blasted away in a massive supernova.
00:34:28But deep in the center, the core falls down what we call a gravitational well.
00:34:36It crushes itself into a single point.
00:34:40A black hole is born.
00:34:44Nothing nearby can escape its pull, not even light.
00:34:52It's hard to imagine just how dense a black hole can be.
00:34:57But I'll try and put it into perspective using something familiar.
00:35:02The Earth.
00:35:08Imagine, piece by piece, I could compress our planet and crush it until gravity took over and it became a black hole.
00:35:22How small would it have to be to vanish down its own gravitational well?
00:35:37From 8,000 miles in diameter, I'd have to crush it to the size of a pea.
00:35:47In my years studying black holes, one of my most unexpected discoveries was that a black hole cannot be perfectly black.
00:35:58For much the same reason as the early universe could not have been perfectly spread out.
00:36:05There is no such thing as perfection.
00:36:10Black holes must give off radiation.
00:36:15The smaller the black hole, the greater the radiation.
00:36:20An even tinier black hole with only the mass of a mountain range would actually shine.
00:36:34Out in space, most black holes are much larger.
00:36:40The smaller ones have around four times the mass of our sun and are 15 miles in diameter.
00:36:48Some are much larger, containing the mass of thousands of suns.
00:36:54And then there are the really big ones.
00:36:59Supermassive black holes that exist at the centers of galaxies like our own.
00:37:10This black hole is thought to have the mass of four million suns and a diameter of 11 million miles.
00:37:21Black holes like these are the heavy hubs around which many galaxies, including the Milky Way, rotate.
00:37:30A kind of stabilizer that gives them form and shape.
00:37:37So eight billion years after the Big Bang, after a long and remarkable run of good luck,
00:37:45we have stars and we have galaxies slowly rotating around giant black holes.
00:37:52Now the scene is set for something close to our hearts.
00:37:57The formation of our sun, the Earth and ultimately us.
00:38:07Our solar system, the place we call home, lies about 26,000 light-years from the center of our galaxy, the Milky Way.
00:38:19Or around two-thirds the way out.
00:38:24The story of how these huge planets came to be orbiting an average yellow star is six billion years long.
00:38:32And since we don't have that much time, I'll speed it up a bit.
00:38:39It starts with a bang.
00:38:46Long ago, an ancient star exploded, littering space with swirling clouds of the materials it had made while it lived and the heavier metals it created as it died.
00:39:02We know this because we can see similar fields of dust out in space today.
00:39:09They are called nebulae, and they are very beautiful.
00:39:15Every nebula is different, and in our case, the clouds contained nitrogen and oxygen and iron and silica and all the other stuff needed to build a world like ours.
00:39:30Then the tireless force of gravity started to pull it all back together, and the heavy engineering that produces planets began.
00:39:41Vast spirals of dust began to form, and at the center of one of these, a rocky planet called Earth started to take shape, built of stardust and assembled by gravity.
00:40:12Fast forward 100 million years, and it had grown into a giant ball, sweeping up billions of tons of celestial debris.
00:40:27This is where the Earth came from, and therefore how you and I began.
00:40:39But our planet would have remained a large, sterile ball of rock and metals and minerals forever, were it not for one more event, one more expression of the forces of nature.
00:40:5793 million miles away, at the heart of the giant nebula, the pressure and temperature of a ball of hydrogen gas had become so great that the atoms were beginning to fuse.
00:41:10A new star, our sun, was coming to life.
00:41:15As the sun ignited, it gave off a huge blast of solar wind, a radioactive gust of energy.
00:41:34This blew all the remaining dust and gas that was left over from the nebula out to the edge of the solar system, which is why everything is nice and orderly today.
00:41:51In the outer reaches of the solar system we have the huge gas planets, Jupiter, Saturn, Uranus and Neptune.
00:42:01Further in are the denser, rockier planets, Mercury, Venus, Mars and, of course, the Earth.
00:42:15Lucky for us, the sun is 865,000 miles in diameter, or just the right size to burn consistently for a very long time, 8 billion years, long enough to allow the next development to take place.
00:42:33Life.
00:42:38Life is one of the strangest phenomena known.
00:42:43In my opinion, it shows that the universe is capable of almost anything.
00:42:51Yet it amazes me that we can know so much about how the universe began many billions of years ago.
00:42:59But we have yet to discover how life itself began.
00:43:05The most likely explanation is probably that we are an accident.
00:43:13Just by chance, some molecules bumped into each other at random, until finally one formed that could copy itself.
00:43:25Then began the slow process of evolution that led to all the extraordinary diversity of life on Earth.
00:43:35Life seems to be simply what matter does, given the right conditions and enough time.
00:43:42I think that life is probably quite common throughout the universe, but that's another tale altogether.
00:43:52As life developed, it changed the planet on which it was born, altering the very fabric of the Earth.
00:44:05After four and a half billion years, the human race arrived on the scene.
00:44:14But one thing often troubles people when they hear this story.
00:44:19How could such an astounding chain of events, which resulted in us, be an accident?
00:44:27Perhaps science has revealed there is some higher authority at work, setting the laws of nature so that our universe, and we, can exist.
00:44:40On the face of it, life does seem to be too unlikely to be just a coincidence.
00:44:48Think about it.
00:44:50The Earth lies at exactly the right distance from the Sun to allow liquid water to flow into the atmosphere.
00:44:57And the Sun just happens to be the right size to burn for billions of years, long enough for life to have evolved.
00:45:07The solar system is littered with all the elements needed for life.
00:45:12And the Earth is just the right size for life.
00:45:16And the Earth is just the right size for life.
00:45:19And the Earth is just the right size for life.
00:45:22The solar system is littered with all the elements needed for life.
00:45:27These elements themselves are only possible because of older stars that have burnt out.
00:45:35These older stars only existed because of a tiny unevenness in the early primordial gas.
00:45:42That was itself produced by a one in a billion imbalance in the sea of particles that came from the Big Bang.
00:45:58So is there a grand designer who lined up all this good fortune?
00:46:05In my opinion, not necessarily.
00:46:08Look at it this way.
00:46:10What if there were other universes, ones not as lucky as ours?
00:46:15Each of these universes could have come from its own Big Bang,
00:46:20with different laws of physics and different conditions.
00:46:26In some, gravity might not exist, and there could be no life.
00:46:32In others, hydrogen might exist.
00:46:34And there could be no life.
00:46:36In others, hydrogen might not fuse, so there would be no stars.
00:46:42And again, no life.
00:46:45And for any number of reasons, universes could have come and gone without producing anything at all.
00:46:56So perhaps we should not be too surprised to find ourselves in a perfect universe,
00:47:01orbiting a perfect sun on a perfect planet,
00:47:05because such perfect places are the only ones where life like us can exist.
00:47:19We are one of the many products of the universe,
00:47:23the result of an ancient and elegant mechanism.
00:47:27But even this remarkable discovery is only just the beginning of what physics can tell us.
00:47:35We can find out what humankind will face in the distant future.
00:47:47And ultimately, we might discover the fate of the universe itself.
00:47:57One reason I love cosmology is that it tells us not only where the vast web of galaxies in our universe came from,
00:48:07but also what lies in store for both the universe and for us.
00:48:14I think it's pretty exciting to be among the first human beings able to look forward for hundreds and even billions of years,
00:48:23maybe as far as the end of time itself.
00:48:30What I see is not only the future of the cosmos we inhabit,
00:48:35but also the enormous challenges our species will face.
00:48:40After all, we are puny organisms compared to the mighty universe that made us.
00:48:46If the Earth that gave us life will not always be the Blue Sanctuary, it is today.
00:49:00The continents of our planet are drifting.
00:49:05Fast forward 75 million years and they will be clustered towards the South Pole.
00:49:10No one knows if the Earth will still be habitable then, but the sad truth is that we may not last long enough to find out.
00:49:20As we gaze into the future, it turns out that the universe is a pretty dangerous place.
00:49:31Just look at our neighborhood.
00:49:34It's littered with billions of asteroids.
00:49:37Ancient remnants left over from the process that built the solar system.
00:49:43The possibility of one of these wiping us out isn't just the stuff of Hollywood disaster movies.
00:49:49The threat from asteroids is real.
00:49:53We've even given some of them names.
00:49:59This one is called Apophis.
00:50:02After a mythical Egyptian demon, a god of darkness and destruction.
00:50:14Discovered in 2004, Apophis is the size of a 100-story skyscraper.
00:50:22It weighs about 20 million tons.
00:50:26Speeding through space at 28,000 miles an hour, ten times as fast as a bullet,
00:50:32it carries almost as much energy as all the world's nuclear weapons combined.
00:50:39And we know roughly where it's headed.
00:50:44The world's largest nuclear power plant is located on the planet's surface.
00:50:50The precise path is not yet fully known.
00:50:56But on April the 13th, 2029, this huge rock is likely to pass within 23,000 miles of the planet's surface.
00:51:07Close enough to pass beneath the Earth's surface.
00:51:10This huge rock is likely to pass within 23,000 miles of the planet's surface.
00:51:17Close enough to pass beneath satellites in orbit around the Earth and give us all the scare.
00:51:30Luckily, there's very little chance that Apophis will actually hit us.
00:51:36But the problem for humanity is that in space, there's always a bigger rock.
00:51:54There are thousands of really large asteroids out here.
00:51:59Some are over ten miles long, the size of Manhattan.
00:52:06An asteroid this size hits the Earth every hundred million years or so.
00:52:29The last one struck the Earth 65 million years ago and probably was responsible for wiping out the dinosaurs.
00:52:43We don't know when the next asteroid will strike, but if it was big enough, it could sterilize our planet.
00:52:51That would be the end of the five billion year long story of life on Earth.
00:52:59But even if we avoid such a natural catastrophe, we could all too easily end up destroying ourselves.
00:53:07In the last 10,000 years, humans have come to dominate the planet.
00:53:14We're so successful that it's tempting to think we are evolution's grand prize.
00:53:21But I believe intelligence is probably overrated.
00:53:26It's not necessarily about intelligence.
00:53:30But I believe intelligence is probably overrated.
00:53:35It's not necessarily a good thing for a species' survival.
00:53:40Bacteria have managed without it for over three billion years.
00:53:47Intelligence, at least in our case, leads to technology.
00:53:54And there are many ways technology could wipe us out.
00:53:58The most obvious, of course, the threat from nuclear weapons.
00:54:05Even if the risk of a nuclear war happening in one year is minuscule, say only one in a million,
00:54:12if we run those odds over a hundred thousand years, the chance of catastrophe falls to one in ten.
00:54:29Personally, I worry that even this might be over-optimistic.
00:54:34Although we are clever enough to have designed such weapons, I'm not sure we are clever enough not to use them.
00:54:43As time marches relentlessly into the future, the universe has other surprises in store.
00:54:53There are some powerful things out there.
00:54:58Some of which could destroy the Earth without any help from us.
00:55:07As the universe continues to dance to its ancient rhythm,
00:55:12stars will come and go in a relentless cycle.
00:55:16And because there are hundreds of billions of stars, there's always one dying in a supernova somewhere.
00:55:23In our galaxy, for instance, a star dies every 50 years or so,
00:55:29which is but the briefest of moments to the universe.
00:55:35It's just about conceivable that a supernova could damage the Earth,
00:55:40if you consider the likelihood over a long enough timescale.
00:55:44One kind of supernova, discovered entirely by accident, is thought to be particularly dangerous.
00:55:56In 1967, when the Cold War was at its height,
00:56:00US military satellites picked up a massive burst of something called gamma radiation.
00:56:07Gamma radiation is the most dangerous type of radiation known.
00:56:12It's also the tell-tale sign of an atomic weapon.
00:56:22Well, the gamma rays detected evidence of a new and powerful Soviet weapon.
00:56:28Where the gamma rays detected evidence of a new and powerful Soviet bomb.
00:56:38Thankfully, the answer was no.
00:56:46After careful analysis of the data,
00:56:49they discovered that the sudden bursts of gamma rays were actually coming from space.
00:56:57Not even the Russians had that kind of technology.
00:57:02Decades later, we still don't have proof of what causes the bursts of radiation.
00:57:09But there's a well-respected theory that they are produced by a special kind of supernova,
00:57:15called a gamma ray burster.
00:57:21What's more, there might be one quite nearby.
00:57:25Hidden within this massive spiral plume of plasma, 8,000 light-years from Earth,
00:57:32is a star called WR104.
00:57:39Deep inside the star itself is a bright sphere,
00:57:43throwing off a shell of hot gas as it nears its end.
00:57:48If this star is what we think it is,
00:57:51then as it dies, it will produce two tightly-focused beams of radiation,
00:57:57one from each pole.
00:58:07And as it dies, it will produce another beam of radiation,
00:58:12one from each pole.
00:58:18The star destroys itself as it produces these beams,
00:58:24which contain more energy than our Sun will produce in its entire life.
00:58:39The brightest known phenomena in the entire Universe.
00:58:48No one is sure if WR104 will do this,
00:58:53or if the beam would strike the Earth.
00:58:56But if so, we could be bathed in high-intensity radiation,
00:59:05with some devastating consequences.
00:59:11The beam would cause spectacular auroras,
00:59:14stripping the ozone from the atmosphere,
00:59:17allowing deadly radiation from the Sun to strike the Earth.
00:59:25It may sound like science fiction,
00:59:28but this could be the second time skies like these have been seen on our world.
00:59:36450 million years ago,
00:59:39over half of all living creatures on the planet
00:59:42were wiped out in a great extinction.
00:59:46One explanation is that a gamma-ray burster
00:59:50irradiated the planet so badly
00:59:53that Earth's ecosystem virtually collapsed.
00:59:57I don't want to worry anyone,
01:00:00but I think it's definitely a good idea for the human race
01:00:04to venture far beyond the Earth.
01:00:07We would be wise to keep our eggs in as many baskets as possible.
01:00:13Thankfully, that process has already begun.
01:00:26In my opinion, the launch of Apollo 11
01:00:30is probably the most important moment in human history.
01:00:33It was a turning point for the universe, too.
01:00:37Life, in the form of us,
01:00:40escaped its home planet
01:00:44and stepped into a new era.
01:00:47A new era of life.
01:00:50A new era of life.
01:00:53A new era of life.
01:00:56A new era of life.
01:00:59A new era of life.
01:01:02And stepped on another surface.
01:01:21The astronauts' footprints stand preserved to this day.
01:01:26A testament to the beginning of what I think could be the next chapter
01:01:31in the story of the cosmos.
01:01:34The spread of life to other parts of the universe.
01:01:44As the universe gets older,
01:01:47we will have to get wiser.
01:01:51I think we'll have to go much further than the Moon
01:01:55at the very least, to Mars.
01:02:03The red planet is likely to play an important part in our evolution
01:02:08and maybe even in the story of the cosmos.
01:02:13It's the second and possibly the most important stepping stone
01:02:17on humanity's journey to the stars.
01:02:26Robot missions to Mars have revealed a spectacularly beautiful
01:02:31yet dangerous and desolate place.
01:02:37I imagine that being a human pioneer here would be an exciting business.
01:02:56For a start, it's cold.
01:02:59It's 50 million miles further from the Sun than the Earth
01:03:04and so it receives half as much warmth.
01:03:07And the temperatures fluctuate wildly.
01:03:11From 80 degrees to minus 200 in a matter of minutes.
01:03:26If the cold doesn't get you, the low gravity will.
01:03:31Mars is just half the size of the Earth
01:03:35and has just 38% of its gravity.
01:03:38Over time, explorers' bones would weaken
01:03:42and their muscles would waste away.
01:03:46Spend long enough on Mars
01:03:49and you could find yourself too weak to safely return to Earth.
01:03:56I'm going to put a big circle around it.
01:03:59The low gravity also means Mars struggles to hold on to an atmosphere.
01:04:04Here, there's nothing more than a thin wisp of carbon dioxide
01:04:08at just one hundredth the pressure of our air.
01:04:20Mars is also bathed in harmful radiation from the Sun.
01:04:25Even though it's further away, unlike Earth,
01:04:29it has no magnetic field and no ozone layer to protect it.
01:04:38Early explorers would have to be careful to minimise their exposure.
01:04:43Perhaps they'd even have to live underground.
01:04:47But one day, I think it'll be possible to drastically alter conditions on Mars,
01:04:54perhaps using space-borne mirrors to supply warmth and power.
01:05:02With perfectly foreseeable technology, much more could become possible.
01:05:17If we could erect giant domes made of glass and plastic to block out the radiation,
01:05:23inside them, we could enrich the atmosphere.
01:05:31Five hundred years from now, which really is a very short time indeed,
01:05:36I think Mars will have its own language, its own currency, its own cuisine.
01:05:42Although I'll bet you, you'll still be able to get a hamburger somewhere.
01:05:51But it's clear that as the universe continues to age,
01:05:55even advances like these will not be enough to guarantee humanity's existence for a very long time.
01:06:12Look further into the future, and ultimately our solar system will follow the same path
01:06:18as countless billions of solar systems before it, and cease to exist.
01:06:27Right now, the Sun is in the middle of its life cycle.
01:06:31During this phase, it is getting gradually hotter and brighter all the time,
01:06:37by about 6% every billion years.
01:06:42In about 5 billion years, the Sun's temperature will have grown to nearly 200 billion degrees.
01:06:56At this point, the Earth will be an unrecognizable ball of molten rock,
01:07:03all life having long since perished.
01:07:07This is our planet's unavoidable destiny.
01:07:12But that's not all the Sun has in store.
01:07:17As it runs out of fuel, the Sun will start to expand, turning into what's called a red giant.
01:07:25It will change from being the object that gave us life to the one that annihilates it.
01:07:32In about 7 billion years, the Sun will be 200 times bigger,
01:07:39about 200 million miles across,
01:07:44so vast it will obliterate the inner planets one after the other.
01:07:49Mercury, Venus, and most probably the lifeless Earth.
01:08:02But as the Universe continues to evolve at its own relentless pace,
01:08:08new opportunities will present themselves to us,
01:08:12if we are able to preserve the life that the Cosmos made.
01:08:32This is Gliese 581 d.
01:08:37It's a large, rocky, Earth-like planet, the nearest known.
01:08:43It's just possible that this world, or one like it,
01:08:48could in the future become home to the human race,
01:08:52a second sanctuary against the unforgiving blackness of space.
01:08:57Discovered in 2007, it's seven times bigger than Earth.
01:09:03It orbits a star smaller and redder than our own,
01:09:08but it lies at just the right distance from its Sun to allow water to exist on the surface.
01:09:17But even if the Sun were to disappear,
01:09:20there is a fundamental problem we will have to overcome.
01:09:28Gliese is a very, very long way away.
01:09:35More than 20 light-years from Earth.
01:09:41It's a very, very long way away.
01:09:45More than 20 light-years from Earth.
01:09:50That's 120 trillion miles.
01:09:56To get some idea of this extraordinary distance and the challenge it presents,
01:10:02I'm going to imagine that we could hitch a ride on the fastest man-made object in existence.
01:10:16Voyager 1 was launched in 1977.
01:10:21Now over 30 years old, it's travelled more than 13 billion miles.
01:10:31Its mission so far has taken it to Jupiter and Saturn.
01:10:37By using their gravity to boost its speed, the little spacecraft has entered the record books.
01:10:47It might not look fast, but Voyager is racing through space at 11 miles a second.
01:10:57On Earth, 11 miles a second looks like this.
01:11:07It's 39,000 miles an hour.
01:11:17At this speed, we could circle the globe one and a half times in an hour.
01:11:25So how long would it take a spaceship travelling at Voyager's speed to get to the nearest Earth-like planet, Gliese?
01:11:37The answer reveals the true scale of the cosmos.
01:11:43For even travelling at 11 miles a second, the journey to Gliese would still take over 350,000 years.
01:11:59I think we have a chance to become a lasting part of the ever-changing Universe
01:12:04and to discover what other wonders it might hold.
01:12:08But to do this, we will have to develop new technology on an enormous scale.
01:12:15And that's going to take some serious engineering.
01:12:23There are many in the field of cosmology who believe, as I do,
01:12:28that finding ways to travel great distances will be essential to keeping humankind alive in an ageing Universe.
01:12:40If we could build a machine capable of travelling to other solar systems, we'd open up a fascinating possibility.
01:12:48The survival of the human race for billions of years.
01:12:59Present-day engineers have begun thinking about the principles of building such a ship.
01:13:05This is what it might look like.
01:13:12It could use atomic energy, or perhaps more exotic fuels such as antimatter, supplying it with enormous amounts of power.
01:13:21Yet I think the main challenges won't be technical.
01:13:26The first will be financial.
01:13:32The cost of constructing an interstellar spacecraft would be huge.
01:13:37And for the society that made it, there would be little payback.
01:13:43They would never see it again.
01:13:46So constructing such a machine will either be the greatest act of generosity in history,
01:13:52or it will have to be funded by the travellers themselves.
01:13:59And that's what I'm going to do.
01:14:02I'm going to build it.
01:14:05I'm going to build it.
01:14:08I'm going to build it.
01:14:12I'm going to build it.
01:14:15And that raises the second problem.
01:14:21Even if it could travel mind-numbingly fast, say a thousand times faster than Voyager,
01:14:2811,000 miles a second,
01:14:32a journey to the nearest star system would still take...
01:14:3973 years.
01:14:46THE MISSION
01:14:51Such a long trip means that at least one whole generation of humans
01:14:57would have to live their entire lives in space.
01:15:01And we couldn't exactly say they had volunteered for the mission.
01:15:05The ethics of sending a human cargo on such a voyage
01:15:10would have to be carefully considered.
01:15:17Unless we could extend human lifespans to long enough to make such massive journeys.
01:15:27And that, I think, is what we will ultimately do.
01:15:34And that's what we end up doing.
01:15:40The process has already begun.
01:15:43As I know from personal experience.
01:15:48My muscles no longer function,
01:15:51although my eyes and my brain are still working pretty well.
01:15:56But technology helps me to move and communicate.
01:15:59In the future, technology will do much more than that for all of us.
01:16:08Within the next thousand years,
01:16:11we will see unprecedented changes in our physical capabilities.
01:16:19Genetic engineering will give us longer lifespans and greater intelligence.
01:16:24Modifying our genes could give us skin that protects us from radiation.
01:16:31The ability to breathe poisonous atmospheres.
01:16:36Resistance to infection.
01:16:43We may even develop sophisticated artificial lifeforms using synthetic DNA.
01:16:49Custom designed for the challenges of space travel.
01:16:55These advances would allow us to survive long journeys and inhospitable worlds.
01:17:04I imagine a time when our descendants spread to planets orbiting other stars all over our galaxy.
01:17:13And perhaps further still.
01:17:15Carrying their biological cargo to solar systems we have yet to discover.
01:17:23Ships like this one could be designed to split up and spread out.
01:17:45A true diaspora of life that would have started with us.
01:18:15As we journey across interstellar space, I'm sure that we will unlock nature's deepest secrets.
01:18:34My great hope is that we will discover how the universe will end and solve the ultimate mystery.
01:18:42Why the universe ever existed at all.
01:18:53I once gave a lecture in Japan where I was asked not to mention the end of the universe in case it affected the Japanese stock market.
01:19:03Well I don't know if or when the universe will end.
01:19:08But for those of you who are nervous about your investments, I think it's a bit early to sell.
01:19:19At 13.7 billion years old, our universe is still in its youth.
01:19:26The earliest date we cosmologists think it could end is 30 billion years from now.
01:19:34There's still plenty of action to come.
01:19:43Even long after our sun has died, new stars will be born.
01:19:48Some of which will have new planets around them.
01:19:51Made of the same atoms that make you and me.
01:19:56Maybe we'll end up as part of some future alien ecosystem.
01:20:01Although that's probably a bit of a long shot.
01:20:05What's true is that we are only the temporary custodians of the particles which we are made of.
01:20:13They will go on to lead a future existence in the enormous universe.
01:20:18Certainly gravity will continue its tireless, incessant work.
01:20:24It will go on shaping the vast strings of galaxies as it has ever since the Big Bang.
01:20:32Using supercomputers we can simulate how gravity, even now, causes galaxies to be attracted to each other.
01:20:39Resulting in vast, slow collisions.
01:20:54Our galaxy will merge with its nearest neighbor, the Andromeda galaxy, in around three million years.
01:21:02Our galaxy will merge with its nearest neighbor, the Andromeda galaxy, in around three billion years.
01:21:11A slow motion collision that will take place over two billion years.
01:21:17The same process is happening all over the cosmos.
01:21:22Entire clusters of galaxies are constantly colliding and reforming.
01:21:29Giant collisions as trillions of stars pull on each other.
01:21:35And a new universe is being created.
01:21:39Gravity is driving the cosmic clockwork as it has done ever since the Big Bang.
01:21:49This is what the universe is capable of.
01:21:53It is capable of creating a new universe.
01:21:57It is capable of creating a new universe.
01:22:01It is capable of creating a new universe.
01:22:05This is what the universe looks like when we are released from time on a human scale.
01:22:20But will this cosmic whirlpool go on forever?
01:22:25As an endless maelstrom of mass and energy, space and time?
01:22:32What an extraordinary question to even be able to ask.
01:22:46I think the solution lies back where we began.
01:22:50With the Big Bang.
01:23:02Ask yourself this.
01:23:04What caused the expansion or inflation of the universe in the first place?
01:23:14When we can answer that and fully understand the Big Bang,
01:23:18we will also learn the fate of the universe.
01:23:23The key to it all is something called dark energy.
01:23:28A mysterious form of energy that pushes space itself apart,
01:23:33even as gravity is making matter clump together.
01:23:40It seems as if dark energy supplied the kick that inflated the universe,
01:23:45although we are not quite sure how.
01:23:50What is certain is that the fate of the universe depends on how this dark energy behaves.
01:23:58If the dark energy slowly weakens, then gravity could get the upper hand.
01:24:05And in 20 billion years or so, the universe would go into reverse
01:24:09and drive everything back to whence it came.
01:24:15In a strange reversal of the Big Bang, space itself would contract.
01:24:22This theory is known as the Big Crunch.
01:24:28In the end, if the theory is right, in 30 billion years from now,
01:24:33all the matter of the universe would be swallowed by a single black hole.
01:24:46The entire universe would exist as one tiny point,
01:24:50much as it was at the instant of the Big Bang.
01:24:58But although that's a neat ending,
01:25:01I think that it's more likely that dark energy will drive the expansion of the universe forever,
01:25:08and that ultimately everything will just keep spreading out until the universe is cold and dark.
01:25:16Everything will become so far apart that even gravity will be defeated.
01:25:21I think a big chill is what we've got in store, not a big crunch.
01:25:29So will this be the end of us and life as we know it?
01:25:34Or will we have figured out how to navigate to a new universe before then?
01:25:40I think we'll only know when we truly understand why the universe exists at all.
01:25:51Perhaps then, when we finally unravel the whole cosmic puzzle,
01:25:57we will become masters, not just of our universe, but the universe next door.
01:26:21Transcription by ESO. Translation by —
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